My company uses GitLab/Jira/Confluence, and two super-important features that make Confluence a winner in my mind are a) a way better story for media embedding (including photos and random uploads like PDFs, but also rich/interactive media such as LucidChart and rendering ticket lists from a Jira filter), and b) the inline discussion/annotation framework that lets you tag/nag people, ask for clarification, etc. A big part of inline discussion is that it's an instant marker for later readers that the content may not be up to date or is under discussion/review, whereas a Markdown file in some repo can have a ticket filed against it, but there's nothing in the repo that alerts a later reader to the existence of that ticket until the problem is actually resolved.

I've always been an advocate for the "markdown in the repo" scheme with CI-generated Sphinx (or whatever) docs, but these features have really won me over to the standalone wiki at least in some cases.